Bluetooth anyone?

Sinking their teeth into a new technology, Kettering students use Bluetooth to analyze the sweet spot on tennis racquets.

It wasn't Wimbledon, but that rewarding ring tone heard when the tennis ball hit the sweet spot made everyone feel like a pro - a professional engineer that is.

That ring tone was the sweet sound of success for the students in Dr. Laura Rust's Electrical Engineering Capstone Class. Capstone classes are for seniors, and are developed to test students' cumulative engineering knowledge.

The assignment was to design and build a device that would detect when a tennis ball hits a racquet's "sweet spot" and transmit this information, via Bluetooth technology, to at least three output devices. "These are the first Kettering students to do an assignment using Bluetooth technology," said Rust.

Their goal was to provide "real-time" feedback to a tennis player regarding the accuracy of their stroke, ostensibly so the player could work on improving technique with each play. The feedback was the ring tone signaling when the sweet spot was struck, the "sweet spot" being the Center of Percussion (COP) or the point of impact where the force of the ball impacting the racquet results in no net force on the player's hand or arm.

The required design consisted of a hardware and software module mechanically attached to a tennis racquet. By detecting the vibration of the racquet head after being struck by a ball, it is possible to determine whether the ball impacted the racquet sweet spot or not, according to Rust. This information was to be sent to the player who was using a Bluetooth headset and to simultaneously transmit this signal to a second BT headset (coach headset) and to an audible output device.

Essentially, students had to put an accelerometer on a tennis racquet. Their devices were designed to pick up different frequencies depending upon where the ball hit the racquet and send this data to a PIC (microcomputer). The PIC did analog to digital conversion of the data and the information was run through a band-pass filter to filter out all frequencies except the ones identified as those in the sweet spot range (100-150 hz).

When the PIC recognized a hit in the sweet spot frequency, it sent a signal to a Bluetooth module, which in turn sent a message to a Bluetooth headset giving a tone or ring to let the person using the racquet know that they had hit the sweet spot.

"This project was important because it integrated Electrical Engineering, Computer Science and Mechanical Engineering," said Ben Koestler, of St. Charles, Minn. "Electrical through the circuit board design, Computer Science through the band-pass filter and Mechanical because we had to package the device to minimize its impact on the user," he added.

Ben and his twin Adam were part of a team of five working on the project for Rust. They and Grant Eberly of North Manchester, Ind., Nick Timkovich, of Grand Rapids, Mich., and Andrew Norton, of Lansing, Mich., had their device sandwiched between two sheets of Plexiglas in the "Y" of the racquet's handle. It added weight and reduced aerodynamics, but it continued to work upon impact, a factor that became important during testing.

"I wouldn't let teams bring duct tape, soldering irons or solder to the testing presentation," said Rust, which meant some teams had one shot to prove their device worked before the batteries or other important parts flew off the racquets upon impact.

"The greatest challenge was dealing with suppliers for the Bluetooth module," joked Koestler. Most of his classmates agreed. One team lost three weeks of valuable time when their circuit board was sent to the wrong mailing address.

That team, consisting of Candace Longton, of Brownstown, Mich., Brian Baker, of East Lansing, Mich., and Leo Manlongat, of Windsor, Ont., had their batteries fall out on impact. The instability of their device during use complicated the presentation of the Bluetooth technology on their racquet.

Not that these devices will be standard issue on tennis racquets anytime soon. They add weight and reduce aerodynamics - but they could help players build muscle from the added weight. "It feels heavier with the device on it," said Dave Stewart, director of Athletics and Recreational Services, of a racket he used to volley balls over the net. Other than the added weight, he said, the device didn't impede his swing.

If engineers can perfect the concept, the work Kettering students had to do for this project may eventually show up in pre-Wimbledon training programs.

Bluetooth Technology: Bluetooth is an industrial specification for wireless personal area networks (PANs). The technology provides a way to connect and exchange information between devices such as mobile phones, laptop computers, desktop computers, printers, digital cameras and video game consoles. This information is sent over a secure, globally unlicensed short-range radio frequency.

Bluetooth is acceptable for situations when two or more devices are in proximity to each other and don't require high bandwidth. It is a radio standard and communications protocol primarily designed for low power consumption, with a short range based on low-cost transceiver microchips in each device.